The invention relates to the improvement of the quiet running of an engine by equalizing the torque components of the individual cylinders as to the total torque of an internal combustion engine. Here, the engine can be a spark-ignition engine or a diesel engine. A detection of the actual torque of a cylinder takes place via an evaluation of the time-dependent course of the rotation of the crankshaft or of the camshaft. A torque correction takes place via an intervention on at least one of the variables: injected fuel quantity, air quantity or ignition time point in a spark-ignition engine, exhaust-gas return rate, injection position or cylinder compression. The term "injection position" relates to the angular position of an injection pulse to a reference point such as top dead center of the piston of a cylinder in a combustion stroke.
A method for cylinder equalization is disclosed in U.S. Pat. No. 4,688,535. In this method, segment times are detected to evaluate the time-dependent course of the rotational movement of the crankshaft or camshaft. Segment times are the times in which the crankshaft or camshaft passes through a predetermined angular region assigned to a specific cylinder. The more uniformly the engine runs, the lesser are the differences between the segment times of the individual cylinders. From the above-mentioned segment times, an index for the rough running of the engine can therefore be formed. In the known method, a controller is assigned to each cylinder of the engine and a rough-running actual value specific to a cylinder is supplied to the controller as an input signal. The rough-running values of several cylinders are averaged to form the desired control value. The mean value serves as the desired value. At the output end, the controller influences the cylinder-specific injection time and therefore the cylinder-individual torque contribution such that the cylinder-individual rough-running actual value approaches the desired value.
Rough-running values, which are obtained from rpm signals, are also used for detecting combustion misfires. Quotients are formed as rough-running values LUT in the method disclosed in U.S. Pat. No. 5,861,553. In the numerator of these quotients, differences of sequential segment times are present and the denominator of these quotients contains the third power of one of the participating segment times. This quotient can be weighted with additional factors as well as be provided with a dynamic correction which considers rpm changes of the entire engine. With respect to the formation of rough-running values, U.S. Pat. No. 5,861,553 is incorporated herein by reference. The sum of these rough-running values, which is formed over one camshaft rotation, is equal to zero for a constant engine rpm.
The detection of defects of the transducer wheel system as well as the detection of the component of the rough running which is based on torsion vibrations of the crank drive and on different energy releases in different cylinders, is known from U.S. Pat. No. 5,822,710.
The detected defects and the above-mentioned rough-running component serve to provide a computed correction of the rough-running values for the detection of combustion misfires. For example, in overrun operation with a six-cylinder engine, the segment times (t1, t2, t3) of the three transducer wheel segments are detected. At each segment time, a corrective value (K1, K2, K3) is formed and additively or multiplicatively coupled to the segment time (Kt1=t1*K1 or t1*K1, . . . ). The corrective values are so determined that the results Kti (wherein i=1 to 3) are equal to each other. Such a correction considerably improves the quality of the detection of combustion misfires which is based on the evaluation of rpm fluctuations.